1. Field of the Invention
This invention relates to a process for forming a functional deposited film containing silicon, particularly a deposited film of polycrystalline silicon to be used for semiconductor devices, photosensitive devices for electrophotography, line sensors for image input, image pickup devices, etc.
2. Related Background Art
For example, for formation of polycrystalline silicon films, the normal pressure CVD method, the LPCVD method, the plasma CVD method, etc., have been primarily used, and, in general, the LPCVD method has been widely been used and industrialized. However, in the method of the prior art, for example, in the LPCVD method, the substrate temperature is high and glass substrates, etc., which are cheap cannot be used, and deposited film having practically useful characteristics cannot be obtained at a low temperature.
Also, in the plasma CVD method, while there is an advantage in of making the substrate temperature lower than the LPCVD method, its reaction process is complicated, and not a few ambiguities existed in the reaction mechanism.
Also, there are a large number of parameters for formation of a deposited film (e.g. substrate temperature, flow rates and their ratios of gases introduced, pressure during film format ion, high frequency power, electrode structure, structure of reaction vessel, evacuation speed, plasma generation system, etc.). The plasma formed by combination of such a large number of parameters may sometimes become unstable to give many especially bad properties to the deposited film formed. Besides, in the plasma CVD method, it is difficult to avoid damages by collision of ions or electrons against the film which is an obstacle against obtaining a film of good quality.
As described above, in formation of a silicon film having polycrystallinity, it has been desired to develop a method for forming a polycrystalline silicon film of good quality with a large area by means of a device of low cost while maintaining its practically useful characteristics and uniformness. These are also applicable to other functional films such as silicon carbide films, silicon nitride films, silicon oxide films, etc.